1. Field of the Art
This invention relates to endoscopes which are in wide use primarily in medical fields, and more particularly to an endoscopic light source connector useful for disconnectibly connecting a light guide of an endoscope to a light source.
2. Prior Art
The endoscopes which are designed to be inserted into dark intracavitary portions of patients for examinations or diagnostic purposes need to be connected to an external light source unit to transmit illuminating light from a source lamp of the light source unit to a particular intracorporeal region under observation through a light guide. For connection to such a light source unit, a light source connector is usually attached to the proximal end of a flexible light guide cable which is extended from a manipulating controller section or main body of an endoscope. Further, in order to transmit the illuminating light from the light source unit down to an illumination window at the distal end of an elongated tubular insert portion of the endoscope, a light guide in the form of a bundle of fiber optics is extended to the illumination window through the flexible light guide cable and the insert portion of the endoscope. The light input end of the light guide is encased in a light guide rod which is protruded from the light source connector and plugged into a socket on the light source unit to connect the light guide thereto.
Since an endoscope is used repeatedly for intracavitary examinations, it must be washed after each use. From a hygienic point of view and for the sake of perfect sterilization, the washing treatment should always include sterilization by the use of a disinfectant. In this regard, for the purpose of enhancing the efficiency of the washing treatment, it has been the usual practice to wash and sterilize an endoscope subsequent to a use by immersing the entire body of the endoscope in a disinfectant liquid for a predetermined time duration, including not only the insert portion of the endoscope but also the manipulating control section and the flexible light guide cable. On such occasions, the light guide rod on the light source connector is susceptible to damages on a light receiving end face of the light guide by contact with the disinfectant liquid particularly in case the light receiving end face of the light guide is in an exposed state.
In this regard, it has been known in the art to protect the light receiving end face of the light guide by fitting a protective glass piece in the light guide rod immediately in front of the light receiving end face of the light guide in such a manner as to provide a hermetically sealed protective cover which keeps the light receiving end face of the light guide from direct contact with a disinfectant washing liquid. In order to guarantee a securer hermetic seal, it is desirable for the cover glass to have an ample seal area on its circumference which engages the inner wall surface of the light guide rod. This requirement has been met by employing a cover glass member which is increased in thickness to such a degree as to generally present a somewhat rod-like shape with an elongated girder portion in the axial direction.
However, a glass cover in the form of an elongated rod-like shape invariably causes a marked drop in light pickup rate at the light receiving end face of the light guide. This is because, of the light rays which are converged toward the light input end of the light guide rod, the light rays of large angles of incidence are allowed to divert toward the inner wall surfaces of the light guide rod without falling directly on the light receiving end face of the light guide. It follows that, in order to let the light rays of large incidence angles reach the light receiving end face of the light guide directly, the protective glass member should desirably have as small a thickness as possible and should have its outer surface located close to the light receiving end face of the light guide. Improvements in these two contradictory requirements, i.e., the hermetic tightness of the cover glass and higher light pickup rate across the cover glass, could be achieved by selecting a glass material of high refractivity for the cover glass. However, high refractivity glass materials are generally inferior in resistance to chemicals and in many cases contain lead or other toxic substances which should be excluded from medical equipments or instruments.